Electromechanically actuated valves can be used on an engine of a vehicle. An issue with such valves is how to reliably capture valves in open or closed positions during a cycle of a cylinder without applying full current. Further, during a condition where a valve is not properly captured in a desired position of a cylinder cycle, it can be desirable to have an approach for resuming scheduled valve operation.
One method to control intake and exhaust valve operation during engine operation is described in U.S. Pat. No. 6,640,756. This method presents a controller that attempts to prevent a degradation of an electromagnetic valve due to execution of valve-stopped operation, without degrading starting response characteristics of an internal combustion engine. Further, the disclosure presents a method to adapt valve driving current when there is no combustion in an engine.
The inventors herein have recognized that the above-mentioned method also can have several disadvantages. Namely, the method inhibits valve stopping when a valve is not operating smoothly. In other words, the controller causes the valves to continue to operate even though the valves are operating erratically. However, since engine emissions, combustion stability, and torque can be affected by valve operation, the above approach can result in degraded emissions and performance.
In addition, the above approach adapts valve drive current while combustion is inhibited in respective cylinders. That is, the approach attempts to compensate for differences in valve operation. However, the current that operates a valve in an inactive cylinder can be different than that in an active cylinder. For example, when a valve is repeatedly commanded from a closed position to an open position in an inactive cylinder, there is little if any pressure difference for the valve to overcome. Consequently, the current that moves the valve along the desired trajectory may not reflect the current used to move the same valve in the presence of cylinder pressure or vacuum. Therefore, the above-mentioned drive current adaptation method may be limited in range and effectiveness.
One embodiment of the present invention includes a method to restart at least an electromechanically actuated valve in at least a cylinder of an internal combustion engine, the method comprising: detecting an error in the desired trajectory of said electromechanical valve during a combustion cycle of said engine; returning said electromechanical valve to said desired trajectory after detecting said error. This method can be used to reduce the above-mentioned limitations of the prior art approaches.
By determining an error in the desired trajectory of a valve and then returning the valve to its desired trajectory, improved engine operation can be obtained. In other words, the above-mentioned method can detect a valve that is off trajectory and take control action that may bring the valve back on trajectory. The valves may continue to operate, but control actions can be initiated to reduce the degradation of emissions, drivability, combustion stability, and torque loss. For example, an intake valve may not open completely during an opening cycle of an intake event. Then the intake valve may be commanded to a closed position. Further, the intake valve opening current may be increased for the next scheduled intake event, thereby improving the possibility of a proper intake valve opening. Naturally, proper intake valve operation can improve engine torque, emissions, and drivability.
In another aspect of the present invention, the present invention provides another method to restart at least an electromechanically actuated valve in at least a cylinder of an internal combustion engine, the method comprising: processing a signal indicative of a valve position; calculating an error between said signal and a predetermined valve position; adjusting a base valve current based on said error; commanding said valve to a predetermined position when said error exceeds a predetermined amount; synchronizing said valve operation with the position of said engine; and operating said valve after said synchronization. This method can be used to reduce the above-mentioned limitations of the prior art approaches.
By determining an off trajectory valve in an operating engine, and adjusting a base valve current in an off trajectory valve, engine operation can be improved through valve current adaptation. In one example, engine operating conditions or valve performance may change from the conditions where base valve currents were established. The above-mentioned method can adjust base valve currents in a manner that may compensate for these changes. This method may provide a better way to determine useful valve currents since the method operates during engine operation.
Further, the method may improve engine emissions and drivability by returning a substantially off-trajectory valve, i.e., a valve position path that deviates from a desired path, to a predetermined position before returning the valve to scheduled operation.
The method has an advantage of improving valve trajectory over a wide engine operating range. By adjusting valve current based on actual engine operating conditions fewer off-trajectory events may occur. Further, the method permits different valve trajectories, based on engine operating conditions, to be compensated.
Another advantage of the method is that automatic valve restarts are possible. For example, if a valve is not captured in a desired open or closed position during engine operation, additional current beyond the predetermined dynamic current may be desirable. As discussed above, during dynamic operation, energy from the decompressing spring can help to compress the opposing spring. If a valve is not captured and is in the mid position additional current, current beyond the dynamic current may be used to return the valve to an open or close position. Such an approach first recaptures the valve to a predetermined position and then resumes the dynamic current profile. In contrast, simply continuing to follow a predetermined dynamic current profile may not be sufficient to restart the valve.
The above advantages and other advantages and features will be readily apparent from the following detailed description of the embodiments when taken alone or in connection with the accompanying drawings.